Long code sequences are widely used in communication systems to spread and despread the data-modulated carrier. Both 1X and 3X long code sequences are used in spread spectrum communication systems.
A 3X long code sequence is typically generated from its 1X counterpart. For example, the method proposed by Laird et al. (see "Additional information on Motorola 3X long code generator," by K. Laird, J. Chen, and F. Zhou (Motorola), TR45.5.3.1/99.04.20.07, April 1999, Savannah, Ga.) as well as that proposed by Ramesh et al. (see "A modified long code generation method for spreading rate 3," by N. Ramesh and Q. Li (Lucent), TR45.5.3.1/99.04.20.08, April 1999, Savannah, Ga.) entail taking shifted versions of the 1X long code at 1.2288 Mchips/sec and interlacing them to generate a 3X long code sequence at 3.6864 Mchips/sec. However, the auto-correlation function of the 3X long code sequences generated by either of the above methods are prohibitively high, leading to undesirable interference problems.
In the method proposed by Laird et al., the magnitude of auto-correlation of the generated 3X sequence can be varied by the degree of shift of the starting 1X sequence thus allowing for improvement in the auto-correlation magnitude. In the method proposed by Ramesh, however, the shift values are unknown, leading to unacceptable auto-correlation levels.
In a publication entitled "Long code generators for 3X systems" (see R. T. Derryberry and Mohit K. Prasad, "Long code generators for 3X systems," TR45.5.3.1 Adhoc/99.04.28.0x, Apr. 28, 1999, Teleconference), the authors describe a scalable method for generating long code sequences. Because the system is scalable, the number of long code generators scales linearly with the type of system in use. For example, the method generates 3 long code sequences for 3X systems, 6 long code sequences for 6X systems, etc. However, the method described by Derryberry et al. requires that multiple long code states be initialized or exchanged during signaling.
Accordingly, it would be advantageous to generate a long code sequence which is not subject to the infirmities of the existing methods and systems.